1. Field of the Invention
The present invention relates to an apparatus for determining a recording mode of a frequency-modulated video signal, and in particular, to an apparatus for sensing a video signal which is recorded on a recording medium in a recording mode under frequency modulation which is possibly of different frequencies from mode to mode and for determining in which recording mode the video signal is recorded. The present invention relates to an apparatus for discriminating between a normal-band recording mode and a high-band recording mode of a still video signal recorded on a recording medium, for example.
2. Description of the Related Art
Modes of recording a still picture signal produced by an electronic still camera, for example, on a high-density magnetic floppy disk include a normal-band recording mode and a high-band recording mode.
The still picture signal includes a luminance signal Y and a chroma signal C. The chroma signal C generally includes color difference signals R-Y and B-Y. According to the normal-band recording mode, the luminance signal Y is adopted to achieve a frequency modulation on a carrier having a center frequency of 7 MHz. The frequency-modulated wave is represented as an Y-RF signal. The color difference signals R-Y and B-Y are respectively used for a frequency modulation of carriers of 1.2 MHz and 1.3 MHz, respectively. The resultant frequency-modulated wave is expressed as an C-RF signal. The signals Y-RF and C-RF are mixed with each other to be recorded on a track of a floppy disk for achieving a still picture recording.
FIG. 5A shows frequency allocations of signals Y-RF and C-RF. The signal Y-RF has a sync tip frequency of 6 MHz, a white peak frequency of 7.5 MHz, and a frequency deviation of 1.5 MHz.
In contrast, in a case where the high-band recording mode is utilized to record a high-resolution still video signal, a carrier adopted to achieve a frequency modulation on the luminance signal Y is set to 9 MHz. As shown in FIG. 5B, the signal Y-RF has a sync tip frequency of 7.7 MHz, a white peak frequency of 9.7 MHz, and a frequency deviation of 2 MHz. The signal C-RF is the same as that of the normal-band recording mode.
The playback systems, particularly, of the FM demodulation circuit also depend exclusively upon the variety of the still video signal recording modes. In consequence, an apparatus capable of reproducing both of the normal-band and high-band signals is provided with normal-band and high-band FM demodulation circuits. Because a floppy disk to be loaded in a playback apparatus does not include an explicit indication of the low-band or high-band recording mode employed for the still picture signal recording, even track by track, when the playback apparatus reads out a video signal from the floppy disk, the apparatus is required to determine the recording mode of the obtained video signal, for selecting an appropriate one of the demodulator circuits. Namely, for the selection between the demodulation circuits, a recording mode of the RF video signal is required to be automatically determined.
As noted above, because the carrier frequency of the frequency modulation is different between the normal and high bands, the RF video signals are demodulated so that a difference appears in the voltage of the demodulated signals between both bands. Determination of the recording mode is possibly achieved by use of the voltage difference. However, this decision procedure is attended with problems that adjustment of a threshold voltage is necessary for the judgement. Moreover, a long period of time is required to attain a relatively stable voltage through the demodulation which extends the judgement or determination processing.